• Korean Journal of Environmental Biology
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• v.40 no.4
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• pp.464-476
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• 2022

In recent years, macroalgal bloom occurs frequently in coastal oceans worldwide. It might be attributed to accelerating climate change. "Green tide" events caused by proliferation of green macroalgae (Ulva spp.) not only damage the local economy, but also harm coastal environments. These nuisance events have become common across several coastal regions of continents. In Korea, green tide incidences are readily seen throughout the year along the coastlines of Jeju Island, particularly the northeastern coast, since the 2000s. Ulva species are notorious to be difficult for morphology-based species identification due to their high degrees of phenotypic plasticity. In this study, to investigate temporal variation in Ulva community structure on Jeju Island between 2015 and 2020, chloroplast barcode tufA gene was sequenced and phylogenetically analyzed for 152 specimens from 24 sites. We found that Ulva ohnoi and Ulva pertusa known to be originated from subtropical regions were the most predominant all year round, suggesting that these two species contributed the most to local green tides in this region. While U. pertusa was relatively stable in frequency during 2015 to 2020, U. ohnoi increased 16% in frequency in 2020 (36.84%), which might be associated with rising sea surface temperature from which U. ohnoi could benefit. Two species (Ulva flexuosa, Ulva procera) of origins of Europe should be continuously monitored. The findings of this study provide valuable information and molecular genetic data of genus Ulva occurring in southern coasts of Korea, which will help mitigate negative influences of green tide events on Korea coast.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.10 no.4
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• pp.70-82
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• 2007

Aiming at nature's early restoring needs to select plant species harmonizing with surrounding environment that fits to restoring goal of ultimately aiming at woody plants dominant vegetation that protect and stabilize surface parts of bared slopes. And it is important to make it assimilated with surrounding natural vegetation by differentiating planning of seed mixtures. Natural Ecological Restoring Construction Methods (JSB Method) was developed to increase the effect of landscape change according to seasons not to simple hydro-seeding by reducing rate of foreign grasses while raising rate of wild flower using. It was considered that using wild flowers that bloom on each season solved the problems of slope landscapes that looks artificial and uninteresting. After researching environmental condition of the slopes, JSB Method has shown that, as of wet-type method, soil is relatively soft and the difference of thickness of plant base soil media affects on the difference of soil hardness. In case of soil hardness of 8.8~17mm, there's dangerousness of slope's collapsing, but it has shown that growth of plant was favorable. For the acidity of soil, most of them are in the type of neutralized soil of more than pH 6. And after analyzing the degree of woody plants dominance, it had shown that lower part was occupied with wild flowers and other herbaceous species like China pin, golden phesant mum, pitcher plant, and middle and upper part was occupied with woody plants like silk-tree, sumac forming multi-layer structure. It can be concluded that the restoration objects of the woody plant vegetation on the roadside slopes can be accomplished successfully by Natural Ecological Restoring Construction Method (JSB method).

• Korean Journal of Ecology and Environment
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• v.47 no.4
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• pp.342-349
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• 2014

This study was conducted to identify the bloom-forming Anabaena strains with two phenotypes (straight-type and coil-type) isolated from North Han River (Sambong-ri Joam-myun) using 16S rDNA sequence. The odor material producing potential was also examined using the geosmin-synthesizing gene cluster. Despite of striking morphological difference of the two stains, resembling A. circinalis and A. crassa species, the phylogenetic analysis using 16S rDNA identified the both strains as a single species of A. circinalis with high genetic similarity (98%~100%). Also, two Anabaena strains showed to possess the geosmin-synthesizing gene cluster, indicating that they are capable of producing the odor substance. This study is the first report that provides the direct evidence of geosmin production in the gene level by A. circinalis in Korea, and provides important basic information to identify the source alga of geosmin increase and its management in North Han River.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.4
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• pp.158-164
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• 2006

Yongdam Lake is the fifth largest artificial lake in Korea newly formed by the first impounding the Yongdam Multi-purpose Dam on December, 2002. Yongdam Lake, with her total water storage of 820 million M/T, is located at the roof-top region of the streams flowing into the just-constructed new Saemankeum Lake. Seasonal succession of phytoplakton in Yongdam Lake might affect cyanobacterial blooms in Saemankeum Lake by inoculating seasonal dominants. During 2002-2003 when the first impounding after the construction of Yongdam Multi-purpose Dam was still undergoing, summer cyanobacterial blooms by Anabaena, Microcystis, and Aphanizomenon were observed. Among these three, filamentous Anabaena is well known to have its species with $N_2-fixing$ ability and special cells such as heterocysts and akinetes as well as the vegetative cells. We established a clonal culture of Anabaena spiroides v. crasse (KNU-YD0310) from the live water samples collected at the bloom site of Yongdam Lake. The N- and P-nutrient requirement of the KNU-YD0310 was explored by the experimental cultivation of the laboratory strain. Ratio of heterocysts to vegetative cells increased as N-deficiency extended with its maximum at $N_2-fixing$ condition. The strain KNU-YD0310 exhibited considerable growth under N-limiting conditions while its growth was proportional to the initial phosphate-P concentration under P-deficient conditions. Under P-limiting conditions akinete density increased, which could be interpreted as an adaptation strategy to survive severe environment by transforming into resting stage. The above eco-physiological characteristics of Anabaena spiroides v. crassa might be useful as an ecological criterion in controlling cyanobacterial blooms at Shaemankeum Lake in near future.

• Korean Journal of Ecology and Environment
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• v.38 no.4 s.114
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• pp.475-481
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• 2005

In an effort to identify a new environment-friendly algicide, we examined the ability of extracts from the leaves and stems of nine Korean oak tree species to inhibit growth of the bloom-forming cyanobacterium, Microcystis aeruginosa. At a concentration of 100 mg $L^{-1}$, five of the oak tree extracts (QAT-L, QAT-5, QAS- L, QGI-5, and QSA- L) decreased the cell density of M. aeruginosa by over 90% for 7 days. At a concentration of 20 mg $L^{-1}$, the same five extracts inhibited the growth of M. aeruginosa by approximately 50%. The minimum concentration of oak tree extracts required for effective inhibition of M. aeruginosa (20 mg $L^{-1}$) is comparable to that of the known algicide, tannic acid (17 mg $L^{-1}$), which is thought to be one of the main active ingredients in the oak tree extract. These findings suggest that oak extracts may be useful as an environment-friendly algicide to control the bloomforming cyanobacterium, M. aeruginosa, in eutrophic waters.

• Korean Journal of Environmental Biology
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• v.38 no.1
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• pp.114-126
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• 2020

Bloom-forming toxic cyanobacteria Microcystis spp. are common in the summer season in temperate freshwater ecosystems. Often, it leads to the degradation of water quality and affects the quality of drinking water. In a previous study, NQ (naphthoquinone) compounds were shown to be effective, selective, and ecologically safe algicides for Microcystis spp. blooms. To analyze the superiority of developed NQ derivatives, we conducted a microcosm experiment using clay, which is frequently used in South Korea. Similar to previous studies, the NQ 40 and NQ 2-0 compounds showed high algicidal activities of 99.9% and 99.6%, respectively, on Microcystis spp. at low concentrations (≥1 μM) and enhanced phytoplankton species diversity. However, when treated with clay, a temporary algicidal effect was seen at the beginning of the experiment that gradually increased at the end. In addition, treatment with the NQ compounds did not affect either the abiotic or biological factors, and similar trends were observed with the control. These results showed that the NQ 2-0 compound was more effective, with no ecosystem disturbance, and more economical than the currently used clay. These results suggest that NQ 2-0 compound could be a selective, economically and ecologically safe algicide to mitigate harmful cyanobacterial blooms in the field.